1. Field of the Invention
The present invention relates to a bearing's component, a heat treatment method thereof, a heat treatment apparatus, and a rolling bearing used for a portion where a long rolling contact fatigue life, an increased anti-crack strength, and a reduced long-term dimensional variation are required, and specifically, to a bearing's component, a heat treatment method thereof, a heat treatment apparatus, and a rolling bearing used for a speed reducer, a drive pinion, a bearing for a transmission and the like.
2. Description of the Background Art
To increase bearing's components in life, a heat treatment is performed. Specifically, for example, in quenching the components they are heated in an ambient RX gas with ammonium gas further introduced therein for carbonitriding their surface layer portion (see Japanese Patent Laying-Open Nos. 8-4774 and 11-101247). This carbonitriding process can generate retained austenite in a microstructure to provide an increased rolling contact fatigue life.
As the above-mentioned carbonitriding process is a diffusion process, it requires a high temperature maintained for a long period of time. As such, increased anti-crack strength is hardly obtained. Furthermore, as more austenite is retained, long-term dimensional variation rate increases, which is also a problem in this carbonitriding process.
Under rolling contact fatigue, an increased life can be ensured, an enhanced anti-crack strength can be provided and an increased long-term dimensional variation rate can be avoided by relying on designing a steel alloy. Relying on designing the alloy, however, increases source material cost disadvantageously.
Future bearing's components will be used in environments exerting large loads at high temperatures. Therefore, they will be required to be operable under larger loads at higher temperatures than conventional. As such, there is a demand for a bearing's component having a longer life under rolling contact fatigue, larger strength and higher dimensional stability.